In the past, various different schemes have been employed to retain magnet material elements, such as permanent magnets or the like for instance, against displacement from assembly positions thereof on a rotatable assembly for a dynamoelectric machine. One such scheme is shown in U.S. Pat. No. 4,327,302 issued Apr. 27, 1982 to Doran D. Hershberger. In this patent, a plurality of magnet material elements in the form of bars are abutted between adjacent pole pieces of a rotatable assembly for a dynamoelectric machine, and such magnet material elements are encapsulated in part by rotor bars cast between the adjacent pole pieces with the bars being integral with opposite end rings also cast on the rotatable assembly.
In other prior art patents, metal and metal alloy sleeves or bands were heat shrunk about a rotor core into displacement preventing engagement with a set of magnet material elements arranged or otherwise seated in assembly positions about the circumference of the rotor core, see for instance U.S. Pat. No. 4,242,610 and U.S. Pat. No. 3,531,670. One of the disadvantages or undesirable features with respect to the above discussed shrinking of metallic bands or sleeves about a rotor core to retain the magnet material elements thereon is believed to be that it was too expensive and too cumbersome in manufacture and resulted in rather hot undesirable work areas. Another disadvantageous or undesirable feature with respect to the above discussed metallic bands is believed to be that such metallic bands may increase rotor core losses due to eddy currents resulting in reduced motor efficiency. Further, it is also believed that such above discussed metallic bands, if formed of steel, may also create a short circuit of the magnetic flux resulting in reduced torque output per unit of current input of the motor.
In the U.S. Pat. No. 3,221,194, a rotor core with permanent magnet material elements arranged thereon was dipped into a plastic bath, and when cured, the plastic formed an encapsulating layer over both the rotor core and permanent magnet material elements securing them together. At least one of the disadvantageous features of this plastic encapsulation of the rotor core and permanent magnet material elements is believed to be that it might involve a rather messy procedure resulting in an undesirable work area.